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Visual C++ CComboBox:
Auto-complete
ComboBox
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Chris Maunder
September 11, 1998
Visual C++ 6.0,
VC++ 2003, VC++ 2005
Download
sample project and source files
I had a need
for a combobox that
would auto-complete,
very much like the URL edit box in the toolbar of Netscape
Navigator. It was actually surprisingly simple since the
base CComboBox is so
rich in functionality.
The basic
idea is that every time the text in the edit box changes,
check to see if there is any text in the drop down list
that is prefixed by this edit box text. Handle the CBN_EDITUPDATE
message to get the text change notifications, and use
GetWindowText() to get the text. CComboBox::SelectString
will look for a string in the list which is prefixed by
the given string, and select it into the edit box. I then
select the portion of text that was added to the users
typed text so that they can continue typing and have the
additions ignored if they wish. That takes care of 90% of
the work.
The only
trick is in handling backspaces and deletes. When a user
hits delete, the text is changed, and the auto-completion
routine will try to restore that text back again. Just
check in PreTranslateMessage for a KEY_DOWN message with a
virtual key of VK_DELETE or VK_BACK, and temporarily
disable the auto-complete mechanism
for those key strokes.
Source
code
#if !defined(AFX_COMBOBOXEX_H__115F422E_5CD5_11D1_ABBA_00A0243D1382__INCLUDED_)
#define AFX_COMBOBOXEX_H__115F422E_5CD5_11D1_ABBA_00A0243D1382__INCLUDED_
#if _MSC_VER >= 1000
#pragma once
#endif // _MSC_VER >= 1000
// ComboBoxEx.h : header file
//
// Copyright (c) Chris Maunder 1997.
// Please feel free to use and distribute.
/////////////////////////////////////////////////////////////////////////////
// CComboBoxEx window
class CComboBoxEx : public CComboBox
{
// Construction
public:
CComboBoxEx();
// Attributes
public:
// Operations
public:
// Overrides
// ClassWizard generated virtual function overrides
//{{AFX_VIRTUAL(CComboBoxEx)
public:
virtual BOOL PreTranslateMessage(MSG* pMsg);
//}}AFX_VIRTUAL
// Implementation
public:
virtual ~CComboBoxEx();
BOOL m_bAutoComplete;
// Generated message map functions
protected:
//{{AFX_MSG(CComboBoxEx)
afx_msg void OnEditUpdate();
//}}AFX_MSG
DECLARE_MESSAGE_MAP()
};
/////////////////////////////////////////////////////////////////////////////
//{{AFX_INSERT_LOCATION}}
// Microsoft Developer Studio will insert additional declarations immediately before the previous line.
#endif // !defined(AFX_COMBOBOXEX_H__115F422E_5CD5_11D1_ABBA_00A0243D1382__INCLUDED_)
// ComboBoxEx.cpp : implementation file
//
// Copyright (c) Chris Maunder 1997.
// Please feel free to use and distribute.
#include "stdafx.h"
#include "ComboBoxEx.h"
#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif
/////////////////////////////////////////////////////////////////////////////
// CComboBoxEx
CComboBoxEx::CComboBoxEx()
{
m_bAutoComplete = TRUE;
}
CComboBoxEx::~CComboBoxEx()
{
}
BEGIN_MESSAGE_MAP(CComboBoxEx, CComboBox)
//{{AFX_MSG_MAP(CComboBoxEx)
ON_CONTROL_REFLECT(CBN_EDITUPDATE, OnEditUpdate)
//}}AFX_MSG_MAP
END_MESSAGE_MAP()
/////////////////////////////////////////////////////////////////////////////
// CComboBoxEx message handlers
BOOL CComboBoxEx::PreTranslateMessage(MSG* pMsg)
{
// Need to check for backspace/delete. These will modify the text in
// the edit box, causing the auto complete to just add back the text
// the user has just tried to delete.
if (pMsg->message == WM_KEYDOWN)
{
m_bAutoComplete = TRUE;
int nVirtKey = (int) pMsg->wParam;
if (nVirtKey == VK_DELETE || nVirtKey == VK_BACK)
m_bAutoComplete = FALSE;
}
return CComboBox::PreTranslateMessage(pMsg);
}
// if we are not to auto update the text, get outta here
if (!m_bAutoComplete)
return;
// Get the text in the edit box
CString str;
GetWindowText(str);
int nLength = str.GetLength();
// Currently selected range
DWORD dwCurSel = GetEditSel();
WORD dStart = LOWORD(dwCurSel);
WORD dEnd = HIWORD(dwCurSel);
// Search for, and select in, and string in the combo box that is prefixed
// by the text in the edit box
if (SelectString(-1, str) == CB_ERR)
{
SetWindowText(str); // No text selected, so restore what was there before
if (dwCurSel != CB_ERR)
SetEditSel(dStart, dEnd); //restore cursor postion
}
// Set the text selection as the additional text that we have added
if (dEnd < nLength && dwCurSel != CB_ERR)
SetEditSel(dStart, dEnd);
else
SetEditSel(nLength, -1);
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